Dylan Hayes, Recreation and Park’s Natural Areas Manager, parked his service truck atop Mt. Davidson a few days ago, lifted a mattock and a pair work gloves from the flatbed and walked to a hillock on the frontier of a stand of eucalyptus trees.

On a south-facing slope he spotted a rarely seen grayish-brown California tarantula, something he’d not seen in his decade serving San Francisco.

“It’s a third bigger in circumference than a silver dollar,” Hayes said, who holds dual bachelor degrees from San Francisco State University in natural resource management and conservation biology.

Bay Area tarantulas live in underground burrows lined with silk for most of their lives. They can be found on Mount Diablo in Contra Costa County, even on Mt. Tamalpais.

“I’d never seen one before in San Francisco, though,” Hayes said, “but I always suspected the spider was here.”

Hayes and his cadre of NAP managers are entrusted with the management of 32 natural open spaces in San Francisco. His job takes him to places such as Glen Canyon, Bernal Hill, Twin Peaks and Mt. Sutro. His mission is to ensure that natural habitats are not over run by inimical invasive weeds that threaten rich biodiversity, and that people, insects, birds and mammals live in harmonic symbiosis with the vegetation that surrounds them.

“I saw the tarantula in open sage scrub,” said Hayes, also the recipient of a MBA in sustainable environment. “I was weeding radish outside the eucalyptus edge and I watched it crawl between several rocks and the duff.”

Tarantulas may appear malevolent, but they are actually very docile spiders, albeit large, reaching five or more inches. Feeding upon smaller arthropods, their venom is not lethal to humans, but is strong enough to subdue their prey. They dig their own burrows or usurp abandoned rodent holes, lining their colonized domiciles with silk produced by the spinnerets at the rear of their abdomen.

“Mt. Davidson coastal sage scrub is essentially the same as the pre-European landscape,” said Hayes. “But tarantulas can’t live in eucalyptus plantations.”

Mindful that avuncular eucalyptus has been in California since early statehood, that it is a sanctuary for raptors and other birds, Hayes has no plan to denude San Francisco’s highest promontory of its Australian import or clear cut any other trees for that matter. Left untended, though, swaths of gum trees can blanket understory with suffocating quilts of deciduous leaves that can mean the death knell for spiders such as the California tarantula, not to mention Mt. Davidson’s palette of ferns, coyote brush and monkey flower that abounds among host grasses.

“The tarantula’s significance is that it is a true relic,” said Hayes. “It reflects the age-old coastal sage and scrub habitat that’s hanging around in San Francisco.”

The NAP’s Significant Natural Resource Areas Management Plan for Mt. Davidson, which will take decades of planned judicious management and cautions implementation, takes the heterogeneity of this valued natural area into account. It is a habitat where NAP believes hummingbirds and chickadees can co-exist in symmetry with red admiral and painted lady butterflies, while day trekkers, accompanied by their canine companions, can stroll along breathtaking paths and trails.

“The California tarantula won’t stick around in the city with constant threats, that’s for sure,” said Hayes, watching the hirsute arachnid inching it way back to its hidey-hole. “It needs protection and stewardship to coexist with us.”